But it remains illegal under federal law. And under state law, possessing small amounts of marijuana is still a civil infraction, meaning it's illegal, but offenders pay a fine and don't go to jail.

Portland Police Chief Michael Sauschuck said at a public forum last week that his department will continue to enforce the federal and state laws, which are not pre-empted by the local one.

But police will use discretion in enforcing them, according to the chief.

That's not good enough for David Boyer, state political director of the Marijuana Policy Project, which advocated for the ordinance.

"We hope officials will respect the will of the voters, and we haven't heard a definitive answer," he said at a Friday morning press conference on the steps of City Hall. "If not, I think we deserve an explanation."

Boyer pointed out that other municipalities abide by similar ordinances in conflict with state and federal laws. For example, in the 33,000-person city of Jackson, Mich., police have pledged to follow a new law, also approved in November, that decriminalizes possession of up to 1 ounce of pot. That's an arrestable offense under Michigan law.

Boyer added that he and other advocates are "keeping an ear to the ground" to learn if the Portland ordinance is not respected by police. But with the law taking effect just hours before the press conference, that didn't appear to be a problem.

"It's kind of hard to do anything until something happens," he said.

Sauschuck downplayed the risk of police enforcement in conflict with the local law.

At the Thursday forum, he presented data showing that marijuana possession accounted for just 1 percent, or 119, of the citations issued by Portland police between July 2011 and July 2013. Of the marijuana citations, 84 involved circumstances under which possession remains illegal, despite the ordinance.

For example, the law does not legalize use or possession in public spaces (including streets, sidewalks, buses, etc.), on school grounds, and in apartment buildings where landlords don't want marijuana used. Sauschuck said only three of the citations were for possession while on private property, and all three involved violations of bail conditions that prohibit drug use.

"I trust our officers. I think these numbers show that they're using their discretion appropriately, judiciously and fairly in their interaction with the public," he said.

While the jury may still be out on the effect of the Portland ordinance, Boyer is also hoping it will help propel change in the state law.

He said the MPP will continue to work with state Rep. Diane Russell, D-Portland, to reintroduce a legalization bill in the Legislature. Unlike the Portland ordinance, Russell's bill would provide a structure for taxing and regulating the drug.

If passed, Maine would be the first state to legalize pot through its elected representatives; the only other states where it is legal, Colorado and Washington, enacted their laws through citizens' initiatives.

The MPP may pursue such an initiative in 2015 if legislation fails, Boyer said. Portland's Green Independent party, also a strong advocate of the ordinance, has not supported Russell's bill.